This invention relates generally to the field of ophthalmic lenses and, more particularly, to intraocular lenses (IOLs).
The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and lens. When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an IOL.
The power of an IOL generally is calculated using measurements of the axial length of the eye and the corneal power of the eye. The axial length is measured either by an ultrasonic A-scan device or an optical device (e.g., IOL Master sold by Zeiss Humphrey) which uses an interferometric method. The corneal power is usually measured by a keratometer. The IOL power calculation is carried out by selecting one of many mathematical formulae involving IOL-related specific constants. For example, the A-Constant for the SRK(trademark) formula, the ACD Constant for the Binkhorst-type formula or the Surgeon Factor for the Holladay formula, etc. IOLS are typically manufactured in 0.5 diopter power increments and the surgeon implants the IOL with the power most closely corresponding with the calculated required power as per the preferred formula with clinically individualized constants developed by the surgeon for the particular IOL and the preferred formula. This method has proven to be acceptable over the years and most patients can be brought to within +/xe2x88x921.00 diopters of the targeted refraction.
During the 1990s, the use of photoablative lasers to reshape the surface of the cornea (photorefractive keratectomy or PRK) or for mid-stromal photoablation (Laser-Assisted In Situ Keratomileusis or LASIK) have been approved by regulatory agencies in the U.S. and other countries. Additional corneal refractive surgical procedures are now being performed widely such as Laser-Assisted Sub-Epithelial Keratectomy or LASEK and contact or non-contact Thermal Keratoplasty or TK/CK. All of these corneal refractive surgical procedures cause an irreversible modification to the shape of the cornea in order to effect refractive changes, and if the correct refraction is not achieved by the first procedure, a second procedure or enhancement must be performed. Additionally, the longterm stability of the correction is somewhat variable because of the variability of the biological wound healing response between patients. As a result, the traditional method of calculating the required power of an IOL based on axial length and central corneal power biometric readings may not be accurate for those eyes that have undergone corneal refractive surgery. In addition, there may be higher order refractive errors in the optical system of the eye that are not adequately addressed with the current IOL power calculation methods and even if these higher order errors are recognized, the current practice of manufacturing IOLS only in discrete spherical (or in the case of toric IOLS, spherical and cylinder) power steps may not enable the surgeon to optimize the patient""s vision.
One patent, U.S. Pat. No. 5,777,719 (Williams, et al.), the entire contents of which being incorporated herein by reference, describes a wavefront-based system for the custom manufacture of intraocular implants, but no specific steps in the manufacturing process are disclosed.
One published WIPO publication, International Patent Application No. PCT/US01/28425 (Publication No. WO 02/22004), the entire contents of which being incorporated herein by reference, describes a system and business model wherein wavefront measurements of the eye are taken and those measurements are used as input for a custom lens manufacturing system. While such a system may be suitable for the manufacture of some types of lenses, such a system is not practical for the manufacture of customized IOLs for several reason. The primary reason for the replacement of the natural lens is the development of a cataract. The opacity of the cataractous lens makes optical wavefront measurement of the eye difficult or impossible. Therefore, the wavefront measurement of the eye must be performed after the natural lens has been removed. Even the most advanced implantable lens manufacturing techniques require a certain amount of time, usually days, to actually make the lens because the lens must be fabricated, possible extractables removed, cleaned, sterilized and aerated. Therefore, there will be some period of time between the removal of the natural lens and the implantation of the IOL, thus requiring two separate surgeries. There are also anatomical changes to the eye that occur once the natural lens has been removed, such as capsule shrinkage, that makes it undesirable for there to be any length of time between the removal of the natural lens and the implantation of the IOL.
In addition, the refractive power of the IOL depends, in large part, to the final position of the lens in the eye. This variable is unknown until the lens is actually implanted in the eye. As a result, even the best surgeons only achieve targeted refraction within +/xe2x88x921.00 diopters in 80% of their patients using current spherical or toric power IOLs for correction of only lower order refractive errors. There is little reason to assume that attempted correction of higher order refractive errors will be any more accurate.
Accordingly, a need continues to exist for an IOL that can be customized to address higher order refractive errors or changes to the cornea as a result of prior corneal refractive surgery. Such customized IOLs are needed for optimum visual outcome in such eyes.
The present invention improves upon the prior art by providing a method of manufacturing an intraocular lens that has been customized to provide optimum vision for an eye with prior corneal refractive surgery. Such a custom manufactured IOL will address not only optical correction requirements as currently met by spherical or toric-shaped IOLs, but will correct higher order optical aberrations using needed optimum customized shapes.
The methods disclosed herein provide optimized prescriptive correction with two embodiments of an IOL. The first embodiment involves the manufacturing of IOLs of fixed shapes for optimum optical correction for a series of groups of patients, each group representing a category of prior corneal refractive surgery, including dioptric correction achieved by the prior surgery. The second embodiment involves the manufacture and implantation of a customized supplementary lens on a primary lens previously implanted in an eye with prior corneal refractive surgery. The primary lens can be similar to currently available spherical or toric-shaped IOLs or can be a custom-shaped IOL as per the first embodiment of the present invention.
Accordingly, one objective of the present invention is to provide a customized intraocular lens.
Another objective of the present invention is to provide a method of manufacturing customized intraocular lenses.
These and other advantages and objectives of the present invention will become apparent from the detailed description and claims that follow.